The present invention r elates generally to a method and system for diagnosing faults in a gas turbine engine without having to rely on subjective, experience-based judgments. The present invention particularly relates to a diagnostic method and system for reliably determining whether the identified faults are related to performance problems in the g as turbine engine or to some other abnoarmality unrelated to engine performance such as faulty test equipment, incorrect calculation methods or adjustment factors, or environ mental factors.
Historically, the detection of test cell related fault s in gas turbine engines has been based on a comparison to sets of limits (minimum or maximum) for various engine performance parameters. These parameters can include engine thrust, exhaust gas temperature and fuel consumption or flow, as well as compressor rotor speeds, air flow through the engine, etc. Gas turbine engines are normally tested in a test cell to assure that the particular engine meets a defined set of limits for each specified parameter. See, for example, U.S. Pat. No. 5,293,775 (Clark et al), issued Mar. 15, 1994. Changes in these sensed parameters are identified by comparison of the parameter values measured for the current engine, relative to the values measured for other prior engines of the same or similar type.
If multiple engine performance parameters are trended, a pattern in these changes can be sufficiently distinct to allow classification (i.e., diagnosis) of a specific fault. Unfortunately, one of the problems in prior test cell diagnostic methods is that changes in the sensed parameters, changes in the test facility, changes in the engine gas path quality and the like can all impact on this capability to accurately determine whether the fault is related to the performance of the engine, or to some other abnormality unrelated to the engine. Some factors impacting on the ability to separate engine related faults, from faults unrelated to the engine, include the data acquisition or testing equipment used, the adaptive equipment for the test cell (i.e., equipment used in place of other equipment normally present when the engine is installed), as well as environmental factors (e.g., air temperature, barometric pressure and relative humidity). A further problem with engine-to-engine comparisons is data scatter (i.e., no trend line or curve can be determined within statistical limits) that can be on the same order of magnitude as the possible engine fault effects to be identified.
Existing test cell diagnostic methods are typically based on trend shift recognition of a single engine performance parameter using an outlier detection logic (i.e., checking for abnormal results that fall outside the trend line or curve as determined by the statistical deviation criteria used). While this method can be effective in identifying specific faults related to engine performance, in some instances, small changes in a single parameter can be missed or can take several sequential occurrences of such events before a specific fault can be identified as being related to engine performance. In addition, because of multiple interactions between the parameters that are sensed or measured, this prior method is not sufficiently effective in identifying whether the potential causes of the fault are engine related or involve some other problem unrelated to the engine such as those involving the test facility and associated equipment, calculation methods or adjustment factors, and environmental factors. This can lead to choosing the wrong or incorrect solution(s) to remedy the supposed cause of the fault.
One reason analysis of these faults has not previously been sequential is because not all of the available information or data is, or can be, incorporated into the analysis. As a result, corrections of the fault are not based on an objective evaluation of the substantive data. Instead, fault diagnosis and correction becomes a subjective judgment requiring a significant amount of experience to choose between possible causes of the detected fault, i.e., is it engine or nonengine related? This makes diagnosis of test cell faults not only more hit-and-miss, but also unusable, or at least not easily usable, by those without the experience with engine performance problems or test cell fault analysis.
Accordingly, it would be desirable, therefore, to have a test cell diagnostic method that provides sequential statistical analysis of multiple gas turbine engine performance parameters and performance conditions, provides reliable identification of whether test cell faults are related to performance problems in the gas turbine engine, or to some other abnormality unrelated to engine performance, provides the ability to incorporate all available prior information or data into the test cell fault analysis, and does not require subjective judgments based on a significant amount of experience with engine performance problems or test cell fault analysis.
The present invention relates to a method and system for reliably diagnosing or evaluating whether faults detected during the testing of a gas turbine engine, particularly in a test facility such as a test cell or stand, are related to the performance problems of the engine or to some other abnormality unrelated to engine performance. The method of the present invention comprises the steps of and the system of the present invention is capable of:
(A) evaluating one performance parameter of the engine under one performance condition to generate a first set of current engine data;
(B) comparing the first set of current engine data to a first set of prior engine data for the one performance condition of the one performance parameter to determine if there is an abnormality;
(C) if an abnormality is detected after comparing the first set of current engine data to the first set of prior engine data, evaluating the one performance parameter under at least two different performance conditions to generate a second set of current engine data;
(D) comparing the second set of current engine data to a second set of prior engine data for the at least two different performance conditions of the one performance parameter to determine if there is an abnormality;
(E) after comparing the second set of current engine data to the second set of prior engine data to determine if there is an abnormality:
(1) if an abnormality is detected, evaluating whether the abnormality is a fault unrelated to the performance of the engine;
(2) if an abnormality is not detected, evaluating the one performance parameter relative to at least one other engine performance parameter under at least one performance condition to generate a third set of current engine data;
(F) comparing the third set of current engine data to a third set of prior engine data for the at least one other engine performance parameter under at least one performance condition to determine if there is an abnormality;
(G) after comparing the third set of current engine data to the third set of prior engine data to determine if there is an abnormality:
(1) if an abnormality is detected, evaluating whether the abnormality is a fault unrelated to the performance of the engine;
(2) if an abnormality is not detected, evaluating whether the abnormality detected in step (C) is a fault related to performance of the engine.
The method and system the present invention provides a number of benefits and advantages, especially with regard to prior test cell diagnostic methods that rely on analysis of a single engine performance parameter. The method and system of the present invention permits the sequential statistical analysis of multiple gas turbine engine performance parameters and performance conditions for greater accuracy and reliability in diagnosing what the fault is related to. In particular, the method and system of the present invention permits reliable identification of whether the faults detected are related to performance problems in the gas turbine engine, or to some other problem or abnormality unrelated to engine performance such as those involving the test facility and associated equipment, calculation methods or adjustment factors, and environmental factors. The method and system of the present invention provides the ability to incorporate as much as is possible or practicable of the available prior information or data used as the reference point for determining whether the fault(s) detected are related (or unrelated) to engine performance. The method of the present invention also permits objective judgments of what the detected fault is related to without the need for significant amounts of experience with engine performance problems or fault analysis.